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  • 1.
    Ahmadi, Mazaher
    et al.
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Moein, Mohammad Mahdi
    Karolinska Inst, Ctr Psychiat Res, Dept Clin Neurosci, SE-17176 Stockholm, Sweden.;Stockholm Cty Council, SE-17176 Stockholm, Sweden..
    Madrakian, Tayyebeh
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Afkhami, Abbas
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Bahar, Soleiman
    Univ Kurdistan, Fac Sci, Dept Chem, Sanandaj, Iran..
    Abdel-Rehim, Mohamed
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Karolinska Inst, Ctr Psychiat Res, Dept Clin Neurosci, SE-17176 Stockholm, Sweden.;Stockholm Cty Council, SE-17176 Stockholm, Sweden..
    Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry2018In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 1095, p. 177-182Article in journal (Refereed)
    Abstract [en]

    Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between - 2.1 to 13.9 for lidocaine, - 4.2 to 11.0 for prilocaine and between - 4.5 to - 2.4 for ropivacaine in plasma samples while the values were ranged from - 4.6 to 1.6 for lidocaine, from - 4.2 to 15.5 for prilocaine and from - 3.3 to - 2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L-1 for all of the studied drugs. The correlation coefficients values were >= 0.995. The limit of detection values were obtained 4 nmol L-1 for lidocaine and prilocaine, and 2 nmol L-1 for ropivacaine.

  • 2.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    A quality process for assessing mathematics in a study programme2018In: Proceedings från 6:e utvecklingskonferensen för Sveriges ingenjörsutbildningar / [ed] Lena Petersson, Kristina Edström, Oskar Gedda, Fredrik Georgsson, Liselott Lycke och Marie Arehag, 2018Conference paper (Refereed)
    Abstract [en]

    We present two methodologies to assess the use of mathematics in a study programme. Firstly, we use a relatively simple methodology to assess how students show their ability to use mathematics in their degree project reports. Secondly, we present a methodology to assess how mathematics is used during a study programme. We have applied the first methodology on the mathematics content in 114 randomly chosen bachelor degree reports from 6 different study programmes within the fields of electrical engineering and computer engineering at KTH. For the 3-year bachelor degree programmes in computer engineering, we find clear deficits in the way students use mathematics in their bachelor degree reports as compared to the other programmes in our study. Through the second methodology, we were able to relate the deficits in the bachelor degree reports to a programme structure where skills in mathematics have not been sufficiently demanded in the engineering courses of the programme. 

  • 3.
    Banuazizi, S. Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Microwave probe stations with throw-dimensional control of the magnetic field to study high-frequency dynamic in nanoscale devices2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 6, article id 064701Article in journal (Refereed)
    Abstract [en]

    We present two microwave probe stations with motorized rotary stages for adjusting the magnitude and angle of the applied magnetic field. In the first system, the magnetic field is provided by an electromagnet and can be adjusted from 0 to similar to 1.4 T while its polar angle (theta) can be varied from 0 degrees to 360 degrees. In the second system the magnetic field is provided by a Halbach array permanent magnet, which can be rotated and translated to cover the full range of polar (theta) and azimuthal (phi) angles with a tunable field magnitude up to similar to 1 T. Both systems are equipped with microwave probes, bias-Ts, amplifiers, and spectrum analyzers, to allow for microwave characterization up to 40 GHz, as well as software to automatically perform continuous large sets of electrical and microwave measurements.

  • 4.
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Determining and Optimizing the Current and Magnetic Field Dependence of Spin-Torque and Spin Hall Nano-Oscillators: Toward Next-Generation Nanoelectronic Devices and Systems2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin-torque and spin Hall nano-oscillators are nanoscale devices (about 100 nm) capable of producing tunable broadband high-frequency microwave signals ranging from 0.1 GHz to over 65 GHz that several research groups trying to reach up to 200 - 300 GHz. Their development is ongoing for applications in high-frequency nanoelectronic devices and systems, such as mobile phones, wireless networks, base stations, vehicle radars, and even medical applications.

    This thesis covers a wide range of characterizations of spin-torque and spin Hall nano-oscillator devices that aim to investigate their current and magnetic field dependency, as well as to suggest improvements in these devices to optimize their application in spintronics and magnonics. The work is primarily based on experimental methods for characterizing these devices by building up new measurement systems, but it also includes numerical and micromagnetic simulations.

    Experimental techniques: In order to characterize the fabricated nanodevices in a detailed and accurate manner through their electrical and microwave responses, new measurement systems capable of full 3D control over the external magnetic fields will be described. In addition, a new method of probing an operational device using magnetic force microscopy (MFM) will be presented.

    Spin-torque nano-oscillators: We will describe remarkable improvements in the performance of spin-torque nano-oscillators (STNOs) that enhance their integration capability with applications in microwave systems. In nanocontact (NC-)STNOs made from a conventional spin-valve stack, though with thicker bottom electrodes, it is found the auto-oscillations can be excited with higher frequencies at lower threshold currents, and with higher output powers. We also find that this idea is useful for tuning spin-wave resonance and also controlling the thermal budget. Furthermore, a detailed study of magnetic droplet solitons and spin-wave dynamics in NC-STNOs will be described. Finally, we demonstrate ultra-high frequency tunability in low-current STNOs based on perpendicular magnetic tunnel junctions(p-MTJs).

    Spin Hall nano-oscillators: Characterizations of spin Hall nano-oscillator(SHNO) devices based on different structures and materials with both conventional and novel methods will be described. A detailed study of the current, temperature, and magnetic field profiles of nanogap SHNOs will be presented. In addition, we show the current and magnetic field dependence of nanoconstriction-based SHNOs.Moreover, it is shown that multiple SHNOs can be serially synchronized, thereby increasing their output power and enhancing the usage of these devices in applications such as neuromorphic computing. We show synchronization of multiple nanoconstriction SHNOs in the presence of a low in-plane magnetic field. Finally, there is a demonstration of the results of a novel method for probing an operationalSHNO using MFM.

  • 5.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Houshang, Afshin
    A. Awad, Ahmad
    Belova, Lyubov M
    Åkerman, Johan
    Magnetic force microscopy of an operational nanodeviceManuscript (preprint) (Other academic)
    Abstract [en]

    We present a new method for probing the spatial profile of an operational magnetic nanodevice using magnetic force microscopy (MFM). We have developed an MFM system by adding a microwave probe station equipped with microwave probe, bias-T, and amplifier to allow electrical and microwave characterization up to 40 GHz during the MFM process. The nanoscale spintronic devices---spin Hall nano-oscillators (SHNOs) based on Pt/NiFe bilayers with a specific design compatible with the developed system---were fabricated and scanned using a Co magnetic force microscopy tip with 10 nm spatial resolution, while a DC current sufficient to exert auto-oscillation flowed. Our results show that this method of developed provides a promising path for the characterization of the spatial profiles of operational nano-oscillators.

  • 6.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Mohseni, Seyed Majid
    R. Sani, Sohrab
    Eklund, Anders
    A. M. Naiini, Maziar
    Malm, B. Gunnar
    Åkerman, Johan
    Control of thermal budget in nanocontact spin-torque nano-oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the influence of the bottom Cu electrode thickness (tCu) in nanocontact spin-torque nano-oscillators (NC-STNOs) based on Si/SiO2/Pd(8)/Cu(tCu)/Co(8)/Cu(7)/NiFe(4.5)/Cu(3)/Pd(3) GMR stacks on the thermal budget of the magnetodynamically active region. Increasing tCu from 10 to 70 nm results in a ~50% reduction in Joule heating in both the Co and NiFe layers, which directly improves the microwave output stability and linewidth. Numerical simulations of the NC-STNO current distribution suggest that this improvement originates from a strongly reduced lateral current spread in the top ferromagnetic layer and a reduction in the device's resistance.

  • 7.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Åkerman, Johan
    Microwave probe stations with three-dimensional control of the magnetic field to study high frequency dynamics in nanoscale devices2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623Article in journal (Refereed)
    Abstract [en]

    We present two microwave probe stations with motorized rotary stages for adjusting the magnitude and angle of the applied magnetic field. In the first system, the magnetic field is provided by an electromagnet and can be adjusted from 0 to ~ 1.4 T while its polar angle (θ) can be varied from 0o to 360o. In the second system the magnetic field is provided by a Halbach array permanent magnet, which can be rotated and translated to cover the full range of polar (θ) and azimuthal (φ) angles with a tunable field magnitude up to ~ 1 T. Both systems are equipped with microwave probes, bias-Ts, amplifiers, and spectrum analyzers, to allow for microwave characterization up to 40 GHz, as well as software to automatically perform continuous large sets of electrical and microwave measurements.

  • 8.
    Berglund, Lars
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Fu, Qiliang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH Royal Inst Technol, Fibre & Polymer Technol, Stockholm, Sweden..
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Yang, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Modification of transparent wood for photonics functions2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 9.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden..
    Boman, Magnus
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. KTH Royal Inst Technol, EECS SCS, Electrum 229, SE-16440 Kista, Sweden.;RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, SeRC, SE-10044 Stockholm, Sweden..
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 10.
    Boucly, Anthony
    et al.
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France..
    Rochet, Francois
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Arnoux, Quentin
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France..
    Gallet, Jean-Jacques
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Bournel, Fabrice
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Tissot, Heloise
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France.
    Marry, Virginie
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Dubois, Emmanuelle
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Michot, Laurent
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Soft X-ray Heterogeneous Radiolysis of Pyridine in the Presence of Hydrated Strontium-Hydroxyhectorite and its Monitoring by Near-Ambient Pressure Photoelectron Spectroscopy2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6164Article in journal (Refereed)
    Abstract [en]

    The heterogeneous radiolysis of organic molecules in clays is a matter of considerable interest in astrochemistry and environmental sciences. However, little is known about the effects of highly ionizing soft X-rays. By combining monochromatized synchrotron source irradiation with in situ Near Ambient Pressure X-ray Photoelectron Spectroscopy (in the mbar range), and using the synoptic view encompassing both the gas and condensed phases, we found the water and pyridine pressure conditions under which pyridine is decomposed in the presence of synthetic Sr2+-hydroxyhectorite. The formation of a pyridine/water/Sr2+ complex, detected from the Sr 3d and N 1s core-level binding energies, likely presents a favorable situation for the radiolytic breaking of the O-H bond of water molecules adsorbed in the clay and the subsequent decomposition of the molecule. However, decomposition stops when the pyridine pressure exceeds a critical value. This observation can be related to a change in the nature of the active radical species with the pyridine loading. This highlights the fact that the destruction of the molecule is not entirely determined by the properties of the host material, but also by the inserted organic species. The physical and chemical causes of the present observations are discussed.

  • 11.
    Burgos-Parra, E.
    et al.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Bukin, N.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Redjai Sani, Sohrab
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Figueroa, A. I.
    Diamond Light Source, Magnet Spect Grp, Didcot, Oxon, England..
    Beutier, G.
    Univ Grenoble Alpes, CNRS, Genoble INP, SIMaP, Grenoble, France..
    Dupraz, M.
    Univ Grenoble Alpes, CNRS, Genoble INP, SIMaP, Grenoble, France..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Duerrenfeld, P.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Le, Q. Tuan
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Mohseni, S. M.
    Shahid Beheshti Univ, Fac Phys, Tehran 19839, Iran..
    Houshang, A.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Cavill, S. A.
    Univ York, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Hicken, R. J.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    van der Laan, G.
    Diamond Light Source, Magnet Spect Grp, Didcot, Oxon, England..
    Ogrin, F. Y.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Investigation of magnetic droplet solitons using x-ray holography with extended references2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 11533Article in journal (Refereed)
    Abstract [en]

    A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [ Co/ Ni] x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (similar to 100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.

  • 12.
    Chung, Sunjae
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Eklund, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
    Iacocca, Ezio
    Department of Applied Mathematics, University of Colorado.
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Mohseni, Seyed Majid
    Department of Physics, Shahid Beheshti University, Tehran 19839, Iran.
    Sani, Sohrab Redjai
    Department of Physics and Astronomy, Uppsala University,.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Effect of canted magnetic field on magnetic droplet nucleation boundariesManuscript (preprint) (Other academic)
    Abstract [en]

    The influence on magnetic droplet nucleation boundaries by canted magnetic elds are investigated and reported. The nucleation boundary condition, In = αAH + BH + C, is determined at different canted angles (0°< θH<20°) using magnetoresistance (MR) and microwave measurements in nanocontact spintorque oscillators (NC-STOs). As θH increased, the nucleation boundary shifts gradually towards higher In and H. The coefficient B of the nucleation boundary equation also nearly doubled as θH increases. On theother hand, the coefficient αA remained constant for all values of θH. These observations can be explained by considering the drift instability of magnetic droplets and the different tilt behaviour of the Co fixed layer induced by different θH.

  • 13. Fan, W.
    et al.
    Fu, Q.
    Qian, Q.
    Chen, Q.
    Liu, W.
    Zhou, X.
    Yuan, H.
    Yue, J.
    Huang, Z.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Southeast University, China.
    Kou, Z.
    Zhai, Y.
    Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 5, article id 056325Article in journal (Refereed)
    Abstract [en]

    Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.

  • 14. Fazlali, Masoumeh
    et al.
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ahlberg, Martina
    Dvornik, Mykola
    R. Sani, Sohrab
    Mohseni, Seyed Majid
    Åkerman, Johan
    Tuning exchange-dominated spin-waves using lateral current spread in nanocontact spin-torque nano-oscillators2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Refereed)
    Abstract [en]

    We present an efficient method to tailor propagating spin waves in quasi-confined systems. We use nanocontact spin-torque nano-oscillators based on NiFe/Cu/Co spin-valves and study the ferromagnetic and spin-wave resonances (FMR and SWR) of both layers. We employ homodyne-detected ferromagnetic resonance spectroscopy, resembling spin-torque FMR, to detect the magnetodynamics. The external field is applied in-plane, giving a parallel configuration of the magnetic layers, which do not provide any spin-transfer torque. Instead, the excitation is caused by the Oersted-field. By varying the thickness of the bottom Cu electrode of the devices, we tune the current distribution in the samples, and thereby the Oersted field, which governs the spin wave characteristics.

  • 15.
    Horio, M.
    et al.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Hauser, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sassa, Y.
    Uppsala Univ, Dept Phys & Astron, SE-75121 Uppsala, Sweden..
    Mingazheva, Z.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sutter, D.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Kramer, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Cook, A.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kobayashi, M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Chikina, A.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Schroter, N. B. M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Krieger, J. A.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland.;Swiss Fed Inst Technol, Lab Festkorperphys, CH-8093 Zurich, Switzerland..
    Schmitt, T.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Strocov, V. N.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Pyon, S.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takayama, T.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takagi, H.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Lipscombe, O. J.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Hayden, S. M.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Ishikado, M.
    CROSS, Tokai, Ibaraki 3191106, Japan..
    Eisaki, H.
    Natl Inst Adv Ind Sci & Technol, Elect & Photon Res Inst, Tsukuba 3058568, Japan..
    Neupert, T.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Matt, C. E.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland.;Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland.;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Chang, J.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 7, article id 077004Article in journal (Refereed)
    Abstract [en]

    We present a soft x-ray angle-resolved photoemission spectroscopy study of overdoped high-temperature superconductors. In-plane and out-of-plane components of the Fermi surface are mapped by varying the photoemission angle and the incident photon energy. No k(z) dispersion is observed along the nodal direction, whereas a significant antinodal k(z) dispersion is identified for La-based cuprates. Based on a tight-binding parametrization, we discuss the implications for the density of states near the van Hove singularity. Our results suggest that the large electronic specific heat found in overdoped La2-xSrxCuO4 cannot be assigned to the van Hove singularity alone. We therefore propose quantum criticality induced by a collapsing pseudogap phase as a plausible explanation for observed enhancement of electronic specific heat.

  • 16.
    Hårdensson Berntsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Götberg, Olof
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Reinvestigation of the giant Rashba-split states on Bi-covered Si(111)2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125148Article in journal (Refereed)
    Abstract [en]

    We study the electronic and spin structures of the giant Rashba-split surface states of the Bi/Si(111)-(root 3 x root 3)R30 degrees trimer phase by means of spin- and angle-resolved photoelectron spectroscopy (spin-ARPES). Supported by tight-binding calculations of the surface state dispersion and spin orientation, our findings show that the spin experiences a vortexlike structure around the (Gamma) over bar point of the surface Brillouin zone-in accordance with the standard Rashba model. Moreover, we find no evidence of a spin vortex around the (K) over bar point in the hexagonal Brillouin zone and thus no peculiar Rashba split around this point, something that has been suggested by previous works. Rather the opposite, our results show that the spin structure around (K) over bar can be fully understood by taking into account the symmetry of the Brillouin zone and the intersection of spin vortices centered around the (Gamma) over bar points in neighboring Brillouin zones. As a result, the spin structure is consistently explained within the standard framework of the Rashba model although the spin-polarized surface states experience a more complex dispersion compared to free-electron-like parabolic states.

  • 17.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Engineering Magnetic Droplets in Nanocontact Spin-Torque Nano-Oscillators2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are nanoscale spintronic devices capable of generating highly tunable broadband microwave signals. In this thesis, I study nanocontact (NC)-based STNOs using strong perpendicular magnetic anisotropy(PMA) free layers, where a novel magnetic soliton—a magnetic droplet—exists. This work is devoted to further understanding the characteristics of the magnetic droplet in diverse magnetic structures, including orthogonal and all-perpendicular(all-PMA) spin valves (SVs) and orthogonal magnetic tunnel junctions (MTJs). The nucleation, transition, and collapse of magnetic droplets are observed, tailored, and analyzed by engineering the magnetic properties of the thin films’ stacks. This thesis consists of three main parts: Orthogonal SVs with [Co/Ni]/Cu/CoxNiFe1−x: Magnetic droplets were first observed in orthogonal SV STNOs. We engineered the fixed layer magnetization Ms,p by cosputtering different compositions of CoxNiFe1−x (x = 0−1). The nucleation boundaries of a magnetic droplet in a current-field phase shift to a lower region as Ms,p decreases. The nucleation boundary is also examined under canted fields in order to better understand the drift instability of the droplets. The observations not only confirm the theoretical predictions of nucleation boundary, but suggest a method for controlling the nucleation boundary. All-PMA SVs with [Co/Ni]/Cu/[Co/Pd]: In contrast to orthogonal SVs,all-PMA NC-STNOs show many novel features. First, thanks to the dramatic improvement in droplet stability that results from using a [Co/Pd] PMA fixed layer, the droplets are directly imaged by a scanning transmission x-ray microscopy(STXM). The transition between the static bubble and magnetic droplet is also observed and imaged. Moreover, to investigate the effect of PMA, He+ irradiation is conducted on the all-PMA NC-STNOs, progressively tuning the PMA. The transitions of the normal FMR-like mode and droplet mode are demonstrated. The behavior of frequency tunability versus PMA is systematically studied. These investigations of all-PMA and irradiated NC-STNOs show that it is feasible to engineer the magnetic properties of STNOs through He+ irradiation. Besides, the dynamic droplets and static bubbles have great potential applications in next-generation information carriers. Orthogonal MTJs with CoFeB/MgO/CoFe: The existence of droplets in orthogonal MTJs is still debated. Instead, the magnetodynamics are investigated here. Very importantly, we find that the frequency tunability is determined by the spin-transfer torque (STT), the voltage-controlled magnetic anisotropy (VCMA), and thermal heating. This paves the way to improving tunability by combining these contributions. This study will contribute greatly to real applications, such as microwave generators and detectors.

  • 18.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ahlberg, Martina
    Department of Physics, University of Gothenburg.
    Afshin, Houshang
    Department of Physics, University of Gothenburg.
    Ferreira, R.
    International Iberian Nanotechnology Laboratory (INL), Braga, Portugal.
    Freitas, P. P.
    International Iberian Nanotechnology Laboratory (INL), Braga, Portugal.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Department of Physics, University of Gothenburg.
    Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctionsManuscript (preprint) (Other academic)
    Abstract [en]

    We demonstrate the magnetodynamics of nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions, with a strong perpendicular magnetic anisotropy free layer and an easy-plane reference layer. First, the static magnetic properties are studied by conducting hysteresis loop and magnetoresistance measurements. Then, we characterize the generated microwave signals by applying dc currents. Field-sweep signals at xed current show a typical FMR-like frequency dependence. Interestingly, for current-sweep measurements, the plot of frequency versus dc current can be fitted well with a symmetric parabolic and an asymmetric linear term. The symmetric behavior is ascribed to the current-induced Joule heating and Oersted elds. The asymmetric dependence is due to the linear perpendicular spin torque (or eld-like torque) and the voltage-controlled magnetic anisotropy. Our observation hints at a route to improving the frequency tunability in future spintronic applications by selectively adding all these contributions.

  • 19.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. NanOsc AB, S-16440 Kista, Sweden..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Diez, Liza Herrera
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France..
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.
    Magnusson, Fredrik
    NanOsc AB, S-16440 Kista, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France.;Spin Ion Technol, 28 Rue Gen Leclerc, F-78000 Versailles, France..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 6, article id 065309Article in journal (Refereed)
    Abstract [en]

    Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%.

  • 20.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics. Department of Physics and Astronomy, Uppsala University.
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Diez, Liza Herrera
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Zahedinejad, Mohammad
    Department of Physics, University of Gothenburg.
    Ravelosona, Dafine
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Department of Physics, University of Gothenburg.
    Experimental evidence of tunable nonlinearity in He+ irradiated spin-torque oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are among the most promising candidates for nanoscale broadband microwave generators. Before this application can be realized, however, enormous efforts are required of researchers to meet the commercial requirements of high-frequency tunability, high power, and narrow linewidth. As the performance of STNOs is mainly attributed to the nonlinearity on the basis of nonlinear auto-oscillator theory, we here systematically study how this nonlinearity is affected by the free-layer's effective magnetization Meff (i.e., the perpendicular magnetic anisotropy, PMA) in STNOs. The PMA is gradually tuned by using different fluences of He+ irradiation. Consequently, the nonlinearity can be continuously tailored from positive to negative. In addition, due to the almost zero nonlinearity, the linewidth shows an improvement of more than two orders of magnitude. This experimental observation is in strong agreement with the theory of nonlinear auto-oscillators. Our study not only confirms the theoretical prediction of nonlinearity, but also indicates the route to be taken towards realizing commercial microwave generators.

  • 21.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Le, Quang Tuan
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Houshang, Afshin
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Using magnetic droplet nucleation to determine the spin torque effciency and asymmetry in Cox(NiFe)1-x thin filmsManuscript (preprint) (Other academic)
    Abstract [en]

    We demonstrate how to extract the material dependent spin torque efficiency (ε) and asymmetry(λ) from the eld{current nucleation boundaries of magnetic droplet solitons in orthogonal nanocontacts in-torque oscillators with Cox(Ni80Fe20)1-x, (x=0{1), fixed layers. As the perpendicular component of the xed layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic elds when the xed layer magnetization μ0Ms,p is tuned from 1.04 to 1.7 T. We then extract ε and λ from tsto the nucleation boundaries and nd that while ε does not vary with composition, λ increases from1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both ε and λ as functions of material composition.

  • 22.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. NanOsc AB, S-16440 Kista, Sweden..
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Houshang, Afshin
    NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Impact of the Oersted Field on Droplet Nucleation Boundaries2018In: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, article id 3104304Article in journal (Refereed)
    Abstract [en]

    We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

  • 23.
    Khymyn, Roman
    et al.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Lisenkov, Ivan
    Oregon State Univ, Dept Elect Engn & Comp Sci, Corvallis, OR 97331 USA.;Northeastern Univ, Elect & Comp Engn Dept, Boston, MA 02464 USA..
    Voorheis, James
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Sulymenko, Olga
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Prokopenko, Oleksandr
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Tiberkevich, Vasil
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Slavin, Andrei
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Ultra-fast artificial neuron: generation of picosecond-duration spikes in a current-driven antiferromagnetic auto-oscillator2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 15727Article in journal (Refereed)
    Abstract [en]

    We demonstrate analytically and numerically, that a thin film of an antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being driven by an external spin-transfer torque signal, can be used for the generation of ultra-short "Dirac-delta-like" spikes. The duration of the generated spikes is several picoseconds for typical AFM materials and is determined by the inplane magnetic anisotropy and the effective damping of the AFM material. The generated output signal can consist of a single spike or a discrete group of spikes ("bursting"), which depends on the repetition (clock) rate, amplitude, and shape of the external control signal. The spike generation occurs only when the amplitude of the control signal exceeds a certain threshold, similar to the action of a biological neuron in response to an external stimulus. The "threshold" behavior of the proposed AFM spike generator makes possible its application not only in the traditional microwave signal processing but also in the future neuromorphic signal processing circuits working at clock frequencies of tens of gigahertz.

  • 24.
    Kjellgren, Björn
    et al.
    KTH, School of Education and Communication in Engineering Science (ECE), Learning, Language and communication.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wingård, Lasse
    KTH, School of Industrial Engineering and Management (ITM).
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Hedin, Björn
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Berglund, Anders
    The Pedagogical Developers Initiative – Sustainable Impact of Falling into Oblivion?2018In: Proceedings of the 14th International CDIO Conference / [ed] Bean Bennedsen, Edström, Hugo, Roslöf, Songer & Yamamoto, Kanazawa: Kanazawa Institute of Technology , 2018, p. 738-747Conference paper (Refereed)
    Abstract [en]

    Between 2014-16, KTH Royal Institute of Technology set aside considerable resources in its biggest pedagogical project to date, the Pedagogical Developers Initiative. The project has been continuously reported on at recent CDIO conferences. While aimed primarily at CDIO Standard 10, enhancement of faculty teaching competence, the project managed, by design as much as through accident, to strengthen many CDIO standards and syllabus items. With the conclusion of the project, the constructive practices and ideas that emerged from the initiative were meant to be incorporated into the regular operations of the university, a task that was delegated to each of KTH’s ten schools. However, even though KTH officially labelled the project a success, the schools have taken a non-uniform approach to this endeavour, as they indeed had done to the project as a whole during its duration. Following up on our earlier reports, and primarily using data from interviews and our own observations, the paper looks at which of the initiative’s ideas and practices have survived the end of the project, in what forms, by what means, and what insights and lessons one can draw from this when designing mechanisms for continuous and sustainable improvement of pedagogical practices at a technical university.

  • 25.
    Kores, C. C.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ismail, N.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Geskus, D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, M.
    Univ Twente, MESA Inst, Opt Sci, NL-7500 AE Enschede, Netherlands..
    Bernhardi, E. H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Surrey, Adv Technol Inst, Guildford GU2 7XH, Surrey, England..
    Temperature Dependence of Spectral Characteristics of Distributed-Feedback Resonators2018In: FIBER LASERS AND GLASS PHOTONICS: MATERIALS THROUGH APPLICATIONS / [ed] Taccheo, S Mackenzie, JI Ferrari, M, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 106830BConference paper (Refereed)
    Abstract [en]

    The spectral response of a distributed-feedback resonator with a thermal chirp is investigated. An Al2O3 channel waveguide with a surface Bragg grating inscribed into its SiO2 top cladding is studied. A linear temperature gradient along the resonator leads to a corresponding variation of the grating period. We characterize its spectral response with respect to wavelength and linewidth changes of the resonance peak. Simulated results show good agreement with the experimental data, indicating that the resonance wavelength is determined by the total accumulated phase shift. The calculated grating reflectivities at the resonance wavelength largely explain the observed changes of the resonance linewidth. This agreement demonstrates that the linewidth increase is caused by the increase of resonator outcoupling losses.

  • 26.
    Laxman, Karthik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kimoto, Daiki
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sahakyan, Armen
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Nanoparticulate Dielectric Overlayer for Enhanced Electric Fields in a Capacitive Deionization Device2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 6, p. 5941-5948Article in journal (Refereed)
    Abstract [en]

    The magnitude and distribution of the electric field between two conducting electrodes of a capacitive deionization (CDI) device plays an important role in governing the desalting capacity. A dielectric coating on these electrodes can polarize under an applied potential to modulate the net electric field and hence the salt adsorption capacity of the device. Using finite element models, we show the extent and nature of electric field modulation, associated with changes in the size, thickness, and permittivity of commonly used nanostructured dielectric coatings such as zinc oxide (ZnO) and titanium dioxide (TiO2). Experimental data pertaining to the simulation are obtained by coating activated carbon cloth (ACC) with nanoparticles of ZnO and TiO2 and using them as electrodes in a CDI device. The dielectric-coated electrodes displayed faster desalting kinetics of 1.7 and 1.55 mg g(-1) min(-1) and higher unsaturated specific salt adsorption capacities of 5.72 and 5.3 mg g(-1) for ZnO and TiO2, respectively. In contrast, uncoated ACC had a salt adsorption rate and capacity of 1.05 mg g(-1) min(-1) and 3.95 mg g(-1), respectively. The desalting data is analyzed with respect to the electrical parameters of the electrodes extracted from cyclic voltammetry and impedance measurements. Additionally, the obtained results are correlated with the simulation data to ascertain the governing principles for the changes observed and advances that can be achieved through dielectric-based electrode modifications for enhancing the CDI device performance.

  • 27.
    Loiko, P.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Surrey, Adv Technol Inst, Guildford GU2 7XH, Surrey, England..
    Stochastic Model of Energy-Transfer Processes Among Rare-Earth Ions2018In: FIBER LASERS AND GLASS PHOTONICS: MATERIALS THROUGH APPLICATIONS / [ed] Taccheo, S Mackenzie, JI Ferrari, M, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 106831XConference paper (Refereed)
    Abstract [en]

    Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully apply it to the example of cross-relaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al2O3:Tm3+ waveguides on silicon intended for lasers operating at similar to 2 mu m. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbours (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al2O3:Tm3+ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of C-CR = 5.83 x 10(-38) cm(6)s(-1), C-ETU1 = 0.93 x 10(-40) cm(6)s(-1), and C-ETU2 = 7.81 x 10(-40) cm(6)s(-1), and determine the laser quantum efficiency eta(q) of excitation of Tm3+ ions in the upper laser level. For the maximum Tm3+ concentration of 5.0 x 10(20) cm(-3) studied experimentally in this investigation, eta(q) reaches 1.73. Furthermore, the transition cross-sections at the pump and laser wavelengths are determined. For the H-3(6) -> F-3(4) transition, the maximum stimulated-emission cross-section is sigma(e) = 0.47 x 10(-20) cm(2) at 1808 nm.

  • 28. Luo, Jun-Wei
    et al.
    Li, Shu-Shen
    Sychugov, Ilya
    Pevere, Federico
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Zunger, Alex
    Absence of redshift in the direct bandgap of silicon nanocrystals with reduced size2017In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 12, no 10, p. 930-932Article in journal (Refereed)
  • 29.
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Linear, Non-Linear, and Synchronizing Spin Wave Modes in Spin Hall Nano-Oscillators2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin Hall nano-oscillators (SHNOs) are nanoscale spintronic devices that generate microwave signals with highly tunable frequency. This thesis focuses on improving the signal quality of nanoconstriction-based SHNOs and also on developing a better understanding of their magnetization dynamics.

    In the first part of the thesis, we fabricate and characterize low-threshold current SHNOs using NiFe/β-W bilayers. Due to the high spin Hall angle of the β-phase W, the auto-oscillation threshold current is improved by 60% over SHNOs based on NiFe/Pt. We also demonstrate low operational current by utilizing W/Co20Fe60B20/MgO stacks on highly resistive silicon substrates. Thanks to the moderate perpendicular magnetic anisotropy (PMA) of Co20Fe60B20, these SHNOs show much wider frequency tunability than SHNOs based on NiFe with no PMA. Performance is further improved by using highly resistive silicon substrates with a high heat conductance, dissipating the generated excess heat much better than sapphire substrates. Moreover, it also means that the fabrication of SHNOs is now compatible with conventional CMOS fabrication, which is necessary if SHNOs are to be used in integrated circuits. In another approach, we attempt to decrease the threshold current of SHNOs based on an NiFe/Pt stack by inserting an ultra-thin Hf layer in the middle of the stack. This Hf dusting decreases the damping of the bilayer linearly but also degrades its spin Hall efficiency. These opposing trends determine the optimum Hf thickness to ≈0.4 nm, at which the auto-oscillation threshold current is minimum. Our achievements arising from these three approaches show a promising path towards the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque.

    In the next chapter, we use both electrical experimentation and micromagnetic simulation to study the auto-oscillating spin wave modes in nanoconstriction-based SHNOs as a function of the drive current and the applied field. First, we investigate the modes under an in-plane low-range field of 40-80 mT, which is useful for developing low-field spintronic devices with applications in microwave signal generation. It is also essential for future studies on the synchronization of multiple SHNOs. Next, using an out-of-plane applied magnetic field, we observe three different modes and demonstrate switching between them under a fixed external field by tuning only the drive current. The flexibility of these nanopatterned spin Hall nano-oscillators is desirable for implementing oscillator-based neuromorphic computing devices.

    In the final part, we study the synchronization of multiple nanoconstriction-based SHNOs in weak in-plane fields. We electrically investigate the synchronization versus the angle of the field, observing synchronization for angles below a threshold angle. In agreement with the experimental results, the spatial profile of the spin waves from the simulations shows that the relative angle between the modes from the nanoconstrictions decreases with decreasing the field angle, thus facilitating synchronization. The synchronization observed at low in-plane fields improves the microwave signal quality and could also be useful for applications such as neuromorphic computing.

  • 30.
    Mazraati, Hamid
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Etesami, Seyyed Ruhollah
    University of Gothenburg.
    Banuazizi, S. Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Houshang, Afshin
    University of Gothenburg.
    Awad, Ahmad A.
    University of Gothenburg.
    Dvornik, Mykola
    University of Gothenburg.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. University of Gothenburg.
    Auto-oscillating spin-wave modes of constriction-based spin Hall nano-oscillators in weak in-plane fieldsManuscript (preprint) (Other academic)
    Abstract [en]

    We experimentally study the auto-oscillating spin-wave modes in Ni80Fe20/β-W constriction-based spin Hall nano-oscillators as a function of bias current, in-plane applied field strength, and azimuthal field angle, in the low-field range of 40-80 mT. We observe two different spin-wave modes: i) a linear-like mode confined to the minima of the internal field near the edges of the nanoconstriction, with weak frequency dependencies on the bias current and the applied field angle, and ii) a second, lower frequency mode that has significantly higher threshold current and stronger frequency dependencies on both bias current and the external eld angle. Our micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the SHNO mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linear-like mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Utilizing intrinsic frequency doubling at zero eld angle we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-eld spintronic oscillators with applications in microwave signal generation and neuromorphic computing.

  • 31.
    Mazraati, Hamid
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. NanOsc AB, SE-16440 Kista, Sweden.
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Houshang, Afshin
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Awad, Ahmad A.
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Dvornik, Mykola
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. NanOsc AB, SE-16440 Kista, Sweden.;;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields2018In: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, no 5, article id 054017Article in journal (Refereed)
    Abstract [en]

    We experimentally study the auto-oscillating spin-wave modes in Ni(80)Fc(20)/beta-W constriction-based spin Hall nano-oscillators as a function of bias current, strength of the in-plane applied field, and azimuthal field angle in the low-field range of 40-80 mT. We observe two different spin-wave modes: (i) a linearlike mode confined to the internal field minima near the edges of the nanoconstriction, and only weakly dependent on the bias current and the applied-field angle, and (ii) a second, lower-frequency mode with significantly higher threshold current and stronger dependence on both the bias current and the externalfield angle. Micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the spin Hall nano-oscillator mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linearlike mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Using intrinsic frequency doubling at zero field angle, we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-field spintronic oscillators with applications in microwave-signal generation and neuromorphic computing.

  • 32.
    Mazraati, Hamid
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Etesami, Seyyed Ruhollah
    University of Gothenburg.
    Houshang, Afshin
    University of Gothenburg.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Dvornik, Mykola
    University of Gothenburg.
    Åkerman, Johan
    University of Gothenburg.
    Contracting vs. expanding spin wave bullets in spin Hall nano-oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    We employ electrical measurements complemented by systematic micromagnetic simulations to reveal the complex dynamics of nanoconstriction-based spin Hall nano-oscillators. In particular, depending on the strength and out-of-plane angle of the applied magnetic field, we observe three distinct types of magnetization auto-oscillation: (a) a linear-like mode localized in the vicinity of the nanoconstriction by the demagnetizing field, (b) a further localized “regular” spin wave bullet, and(c) a “large” bullet that fills the entire area of the nanoconstriction. Although it has been assumed for some time that bullets only emerge if the nonlinearity of the system is negative (corresponding to the attraction of magnons), our results demonstrate that, in patterned films, they could be sustained even if the nonlinearity of the system is positive (corresponding to the repulsion of magnons). So, in contrast to the regular spin wave bullet, the auto-oscillation volume of its novel large counterpart enlarges, with the amplitude enhancing their drift stability and, correspondingly, reducing their linewidth. We demonstrate that tuning can be achieved between the observed modes at a fixed external field by changing only the drive current, thanks to the amplitude-dependent nonlinearity of the auto-oscillations. This flexibility of nanopatterned spin Hall nano-oscillators is desirable to achieve synaptic functionality in oscillator-based neuromorphic computing devices.

  • 33.
    Mazraati, Hamid
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Muralidhar, Shreyas
    Etesami, Seyyed Ruhollah
    Dvornik, Mykola
    Zahedinejad, Mohammad
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI).
    Chung, Sunjae
    Awad, Ahmad A.
    Åkerman, Johan
    In-plane field angle dependence of mutually synchronized constriction based spin Hall nano-oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    We study mutual synchronization phenomena in multiple nanoconstriction-based SHNOs under weak in-plane fields down to μ0H = 30 mT and investigate the angular dependence of the synchronization condition. We compare double nanoconstriction and multiple nanoconstrictions with different spacings of 300 and 900 nm between the constrictions. For all the tested devices, we observe clear evidence of mutual synchronization of individual nanoconstrictions (NCs) only for angles smaller than a critical angle. This critical angle is higher for the 300 nm spacing than for the 900 nm spacing as a result of the stronger synchronization arising from the shorter distance. Direct inspection of the spin waves using μ-BLS maps confirms synchronization of the double nanoconstrictions. Alongside the synchronization, we observe a strong second harmonic that could be interpreted as a sign that the synchronization is mediated by the propagation of the second harmonic of the spin waves. Micromagnetic simulation explains the synchronization at the lower angles by the direction of the spatial profile of the modes and confirms the role of exchange coupling in the synchronization of nanoconstriction-based SHNOs.

  • 34.
    Mazraati, Hamid
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Zahedinejad, Mohammad
    University of Gothenburg.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. University of Gothenburg.
    Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 9, p. 092401-Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of hafnium (Hf) dusting on the magnetodynamical properties of NiFe/Pt bilayers using spin-torque-induced ferromagnetic resonance measurements on 6 μm wide microstrips on high-resistive Si substrates. Based on two series of NiFe(tNiFe)/Hf(tHf)/Pt(5) stacks, we first demonstrate that the zero-current magnetodynamic properties of the devices benefit from Hf dusting: (i) the effective magnetization of the NiFe layer increases by 4%–8% with Hf present and (ii) the damping α decreases linearly with tHf by up to 40%. The weaker anisotropic magnetoresistance (AMR≈0.3%–0.4%) of the 3 nm NiFe series is largely unaffected by the Hf, while the stronger AMR of the 5 nm NiFe series drops from 0.7% to 0.43% with increasing tHf. We find that the spin Hall efficiency ξSH is independent of the NiFe thickness, remaining unaffected (ξSH = 0.115) up to tHf = 0.4 nm and then decreasing linearly for higher tHf. The different trends of α and ξSH suggest that there is an optimum Hf thickness (≈0.4 nm) for which the threshold current for auto-oscillation should have a minimum, while the much lower damping should improve mutual synchronization. Our results also indicate that the spin-orbit torque is entirely damping-like with no field-like torque component. Finally, the internal spin Hall angle of Pt is estimated to be θSH = 0.22 by calculating the transparency of the interface.

    The full text will be freely available from 2019-08-29 14:46
  • 35. Paul, S.
    et al.
    Iuşan, D.
    Thunström, P.
    Kvashnin, Y. O.
    Hellsvik, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pereiro, M.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Knut, R.
    Phuyal, D.
    Lindblad, A.
    Karis, O.
    Sanyal, B.
    Eriksson, O.
    Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed)
    Abstract [en]

    Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

  • 36.
    Paulraj, Alagar Raj
    et al.
    KTH Royal Inst Technol, Dept Chem Engn, SE-10044 Stockholm, Sweden..
    Kiros, Yohannes
    KTH Royal Inst Technol, Dept Chem Engn, SE-10044 Stockholm, Sweden..
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Johansson, Malin B.
    Uppsala Univ, Angstrom Lab, Dept Chem, Div Phys Chem, POB 523, SE-75120 Uppsala, Sweden..
    NiFeOx as a Bifunctional Electrocatalyst for Oxygen Reduction (OR) and Evolution (OE) Reaction in Alkaline Media2018In: CATALYSTS, ISSN 2073-4344, Vol. 8, no 8, article id 328Article in journal (Refereed)
    Abstract [en]

    This article reports the two-step synthesis of NiFeOx nanomaterials and their characterization and bifunctional electrocatalytic activity measurements in alkaline electrolyte for metal-air batteries. The samples were mostly in layered double hydroxide at the initial temperature, but upon heat treatment, they were converted to NiFe2O4 phases. The electrochemical behaviour of the different samples was studied by linear sweep voltammetry and cyclic voltammetry on the glassy carbon electrode. The OER catalyst activity was observed for low mass loadings (0.125 mg cm(-2)), whereas high catalyst loading exhibited the best performance on the ORR side. The sample heat-treated at 250 degrees C delivered the highest bi-functional oxygen evolution and reduction reaction activity (OER/ORR) thanks to its thin-holey nanosheet-like structure with higher nickel oxidation state at 250 degrees C. This work further helps to develop low-cost electrocatalyst development for metal-air batteries.

  • 37.
    Pollnau, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Department of Electrical and Electronic Engineering, Advanced Technology Institute, University of Surrey, Guildford, United Kingdom.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Novel aspects of the Fabry-Pérot resonator2018In: Advanced Study Institute on NATO ASI on Quantum Nano-Photonics, Springer, 2018, p. 277-295Chapter in book (Refereed)
    Abstract [en]

    We systematically characterize the Fabry-Pérot resonator. We derive the generic Airy distribution of a Fabry-Pérot resonator, which equals the internal resonance enhancement factor, and show that all related Airy distributions are obtained by simple scaling factors. We verify that the sum of the mode profiles of all longitudinal modes generates the Airy distribution. Consequently, the resonator losses are quantified by the linewidths of the underlying Lorentzian lines and not by the measured Airy linewidth. We introduce the Lorentzian finesse which provides the spectral resolution of the Lorentzian lines, whereas the usually considered Airy finesse quantifies the performance of the Fabry-Pérot resonator as a scanning spectrometer. © Springer Nature B.V. 2018.

  • 38.
    Saoud, Khaled
    et al.
    Virginia Commonwealth Univ Qatar, Liberal Arts & Sci, Doha, Al Doha, Qatar..
    Al Soubaihi, Rola
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Self-sustaining and hysteresis behavior of low-temperature CO oxidation on mesoporous Pd/SiO2 aerogel s catalyst under dynamics conditions2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Article in journal (Other academic)
  • 39. Shu, J.
    et al.
    Zhang, X.
    Wang, P.
    Chen, R.
    Zhang, H.
    Li, D.
    Zhang, Pei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. National Laboratory of Solid State Microstructures, Department of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China.
    Xu, J.
    Monte-Carlo simulations of optical efficiency in luminescent solar concentrators based on all-inorganic perovskite quantum dots2018In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 548, p. 53-57Article in journal (Refereed)
    Abstract [en]

    Luminescent solar concentrator (LSC) devices emerge as a promising technology to reduce the cost of electricity generated by photovoltaic solar cells. Here, we demonstrate the detailed fabrication process of non-crystalline LSC prototype devices based on all-inorganic perovskite quantum dots (QDs) for the first time. The as-prepared all-inorganic perovskite QDs show many advantages, such as tunable absorption spectrum over the entire visible spectral region, high photoluminescence (PL) quantum yield (QY) up to 50%, and narrow emission line widths with FWHM (full width at half maximum) of 17–26 nm, which may greatly improve the optical efficiency of LSC prototype devices. On the optimal doping concentrations, Monte Carlo ray-tracing simulations indicate the LSC prototype devices have an extremely high average optical efficiency, which is 1.22% for CsPbCl3 QDs, 5.43% for CsPbBr3 QDs, and 7.39% for CsPbI3 QDs, respectively. We anticipate these potential high-efficiency LSC prototype devices based on perovskite QDs will shed light on future research of large-scale and high-performance LSCs applications.

  • 40.
    Sulymenko, Olga
    et al.
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Prokopenko, Oleksandr
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Lisenkov, Ivan
    Northeastern Univ, Dept Elect & Comp Engn, Boston, MA 02115 USA..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tyberkevych, Vasyl
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Slavin, Andrei N.
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Khymyn, Roman
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Ultra-fast logic devices using artificial "neurons" based on antiferromagnetic pulse generators2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 124, no 15, article id 152115Article in journal (Refereed)
    Abstract [en]

    It has been shown previously that spin-Hall oscillators based on current-driven bi-layered film structures containing an antiferromagnet (AFM) and a normal metal can generate ultra-short (similar to 2 ps) "spike-like" pulses in response to an external current stimulus of a sufficient amplitude, thus operating as ultra-fast artificial "neurons." Here, we report the results of numerical simulations demonstrating that a single AFM "neuron" can perform the logic functions of OR, AND, MAJORITY, or Q-gates, while a circuit consisting of a small number n < 5 of AFM "neurons" can function as a FULL-ADDER or as a dynamic memory loop with variable clock frequency. The clock frequencies of such AFM-based logic devices could reach tens of GHz, which make them promising as base elements of future ultra-fast high-efficiency neuromorphic computing. 

  • 41.
    Vazquez-Cordova, Sergio A.
    et al.
    Univ Twente, MESA Inst, Opt Sci, POB 217, NL-7500 AE Enschede, Netherlands..
    Aravazhi, Shanmugam
    Univ Twente, MESA Inst, Integrated Opt Microsyst, POB 217, NL-7500 AE Enschede, Netherlands..
    Grivas, Christos
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Yong, Yean-Sheng
    Univ Twente, MESA Inst, Opt Sci, POB 217, NL-7500 AE Enschede, Netherlands..
    Garcia-Blanco, Sonia M.
    Univ Twente, MESA Inst, Opt Sci, POB 217, NL-7500 AE Enschede, Netherlands..
    Herek, Jennifer L.
    Univ Twente, MESA Inst, Opt Sci, POB 217, NL-7500 AE Enschede, Netherlands..
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Twente, MESA Inst, Integrated Opt Microsyst, POB 217, NL-7500 AE Enschede, Netherlands..
    High gain in erbium-doped channel waveguides2017In: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC), IEEE , 2017Conference paper (Refereed)
  • 42. Vázquez-Co´rdova, S. A.
    et al.
    Aravazhi, S.
    Grivas, C.
    Yong, Y. -S
    Garci´a-Blanco, S. M.
    Herek, J. L.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    High gain in erbium-doped channel waveguides2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
  • 43. Yong, Y. -S
    et al.
    Aravazhi, S.
    Vázquez-Co´rdova, S. A.
    Herek, J. L.
    Garci´a-Blanco, S. M.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Temperature dependence of transition cross sections in rare-earth-doped laser materials2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
  • 44.
    Yong, Yean-Sheng
    et al.
    Univ Twente, MESA Inst Nanotechnol, Opt Sci Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Aravazhi, Shanmugam
    Univ Twente, MESA Inst Nanotechnol, Integrated Opt Microsyst Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Vazquez-Cordova, Sergio A.
    Univ Twente, MESA Inst Nanotechnol, Opt Sci Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Herek, Jennifer L.
    Univ Twente, MESA Inst Nanotechnol, Opt Sci Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Garcia-Blanco, Sonia M.
    Univ Twente, MESA Inst Nanotechnol, Opt Sci Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Twente, MESA Inst Nanotechnol, Integrated Opt Microsyst Grp, POB 217, NL-7500 AE Enschede, Netherlands..
    Temperature Dependence of Transition Cross Sections in Rare-earth-doped Laser Materials2017In: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC), IEEE , 2017Conference paper (Refereed)
  • 45.
    Zahedinejad, M.
    et al.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics. NanOsc AB, S-16440 Kista, Sweden.
    Fulara, H.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Yue, J.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Awad, A. A.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden.
    CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 13, article id 132404Article in journal (Refereed)
    Abstract [en]

    We demonstrate low-operational-current W/Co20Fe60B20/MgO spin Hall nano-oscillators (SHNOs) on highly resistive silicon (HiR-Si) substrates. Thanks to a record high spin Hall angle of the beta-phase W (theta(SH) = -0.53), a very low threshold current density of 3.3 x 10(7) A/cm(2) can be achieved. Together with their very wide frequency tunability (7-28GHz), promoted by a moderate perpendicular magnetic anisotropy, HiR-Si/W/CoFeB based SHNOs are potential candidates for wide-band microwave signal generation. Their CMOS compatibility offers a promising route towards the integration of spintronic microwave devices with other on-chip semiconductor microwave components.

    The full text will be freely available from 2019-03-29 11:56
  • 46.
    Zhang, Miao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH Royal Institute of Technology.
    Silicon Nanopore Arrays: Fabrication and Applications for DNA Sensing2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanopore biomolecule sensing and sequencing has emerged as a simple but powerful tool for single molecule studies over the past two decades. By elec- trophoretically driving single molecules through a nanometer-sized pore, often sitting in an insulating membrane that separates two buffer solutions, ionic current blockades can be detected to reveal rich information of the molecules, such as DNA length, protein size and conformation, even nucleic acid se- quence. Biological protein pores, as well as solid-state nanopores have been used, but both suffer from relatively low throughput due to the lack of abil- ity to scale up to a large array. In this thesis, we tackled the throughput issue from the fabrication aspect as well as from the detection aspect, aim- ing at a parallel optical single molecule sensing on an array of well-separated nanopores.

    From the fabrication aspect, several lithography-based self-regulating meth- ods were tested to obtain nanopore arrays in silicon membranes, including anisotropic KOH etching, thermal oxidation-induced pore shrinkage, metal- assisted etching and electrochemical etching. Among those, the most success- ful method was the electrochemical etching of silicon. By electron-beam or photo lithography, the positions of the pores were defined on a silicon mem- brane. Followed by anisotropic KOH etching, inverted pyramids were formed as etching pits. The nanopores were then formed by anodic etching of silicon in HF. Using this concept, the size of the pores does not depend on the lithog- raphy step; only the positions of pores were defined by lithography. In this way, an array of ∼ 900 pores with an average entrance diameter of 18 ± 4 nm was fabricated on a 120 μm × 120 μm membrane.

    From the detection aspect, parallel readout of fluorescence signals from the labelled DNA molecules while translocating through an array of nanopores was performed using a wide-field microscope with a relatively fast CMOS camera recording at 1 KHz frame rate. Statistics of duration and frequency of the translocation events were extracted and studied. It was found that the event duration decreases with rising excitation laser power. This can be attributed to a laser-induced heating effect. Simulation suggested that a sig- nificant thermal gradient was generated at the pore vicinity by the excitation laser due to photon absorption by the silicon membrane. Such temperature rise affects all mass transport in a solution via a viscosity change. The ther- mal effect has also been proven by that conductance of an array of nanopores scales with the laser power. The thermal effect on the translocation frequency has been studied systematically as well. Due to thermophoresis of DNA in a thermal gradient, the thermophoretic force serves as a repulsion force, op- posing the electrophoretic force at the pore vicinity, depleting molecules away from the pore. Because of the molecule-size-dependent thermal depletion, a size-dependent translocation frequency was observed. This can be potentially used for a high throughput molecule sorting by adjusting the balance between the thermophoretic force and the electrophoretic force.

  • 47.
    Zhang, Miao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH.
    Ngampeerapong, Chonmanart
    Redin, David
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Ahmadian, Afshin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Thermophoresis-Controlled Size-Dependent DNA Translocation through an Array of Nanopores2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 5, p. 4574-4582Article in journal (Refereed)
    Abstract [en]

    Large arrays of nanopores can be used for high-throughput biomolecule translocation with applications toward size discrimination and sorting at the single-molecule level. In this paper, we propose to discriminate DNA length by the capture rate of the molecules to an array of relatively large nanopores (50–130 nm) by introducing a thermal gradient by laser illumination in front of the pores balancing the force from an external electric field. Nanopore arrays defined by photolithography were batch processed using standard silicon technology in combination with electrochemical etching. Parallel translocation of single, fluorophore-labeled dsDNA strands is recorded by imaging the array with a fast CMOS camera. The experimental data show that the capture rates of DNA molecules decrease with increasing DNA length due to the thermophoretic effect of the molecules. It is shown that the translocation can be completely turned off for the longer molecule using an appropriate bias, thus allowing a size discrimination of the DNA translocation through the nanopores. A derived analytical model correctly predicts the observed capture rate. Our results demonstrate that by combining a thermal and a potential gradient at the nanopores, such large nanopore arrays can potentially be used as a low-cost, high-throughput platform for molecule sensing and sorting.

  • 48. Zhang, X.
    et al.
    Chen, R.
    Wang, P.
    Shu, J.
    Zhang, H.
    Song, H.
    Xu, J.
    Zhang, Pei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Nanjing University, Nanjing, China.
    A soft chemistry-based route to enhanced photoluminescence of terbium ions and tin oxide nanocrystals codoped silica thin films2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 452, p. 96-101Article in journal (Refereed)
    Abstract [en]

    Tb3+ ions and SnO2 nanocrystals (NCs) codoped silica films are fabricated by a soft chemistry-based approach. Via precise adjustment of Sn amounts in precursors, the size and number density of SnO2 NCs can be well controlled by a restrictive crystallization process. The characteristic emission intensity of Tb3+ ions at 541 nm can be greatly enhanced by two orders of magnitude if sensitized by SnO2 NCs with optimized size and number density. Photoluminescence excitation spectra of the films containing different Sn amounts indicate the non-radiative energy transfer process that takes place between Tb3+ ions and surface of SnO2 NCs. The photoluminescence intensity decay curves suggest two kinds of possible occurrence states of Tb3+ ions in codoped samples. All these results suggest the SnO2 NCs represent ideal sensitizers to effectively promote photoluminescence efficiency of Tb3+ ions. Particularly, the soft chemistry-based method reported here is very flexible for the fabrication of rare earth ions doped amorphous thin films, permitting the precise control of size and number density of NCs as sensitizers. We anticipate this fabrication strategy greatly enriches the techniques for the preparation of thin films, providing great promise for the realization of on-chip integration of silica-based optical lasers and amplifiers.

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